Clean up some exceptions, phpdoc

Lib/Exception/AuthenticationException.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace BSR\Lib\Exception;
+
+/**
+ * This exception should be raised when an error
+ * related to the authentication mechanism arise.
+ *
+ * @package BSR\Lib\Exception
+ */
+class AuthenticationException extends WebException {
+    const USER_NOT_FOUND = 200;
+    const BAD_LOGIN = 201;
+    const AUTHENTICATION_FAILED = 202;
+}

Lib/Exception/BookNotFoundException.php

@@ -2,8 +2,14 @@
 
 namespace BSR\Lib\Exception;
 
+/**
+ * This exception should be raised when trying to access or
+ * manipulate a non-existing book.
+ *
+ * @package BSR\Lib\Exception
+ */
 class BookNotFoundException extends WebException {
     public function __construct($code) {
-        parent::__construct('BookNotFound', "The book with code $code was not found", -404);
+        parent::__construct('BookNotFound', "The book with code $code was not found.", 404);
     }
 }

Lib/Exception/UsageException.php

@@ -2,4 +2,18 @@
 
 namespace BSR\Lib\Exception;
 
-class UsageException extends WebException {}
+/**
+ * This exception should be raised by the WebService engine when
+ * there is an error preventing the correct calling of a method.
+ *
+ * @package BSR\Lib\Exception
+ */
+class UsageException extends WebException {
+    const NO_ARGS = 100;
+
+    const MISSING_METHOD = 101;
+    const BAD_METHOD = 102;
+
+    const TOO_FEW_ARGS = 103;
+    const TOO_MANY_ARGS = 104;
+}